1. Field of the Invention
The present invention relates to a method for forming photoresist patterns in fabrication of semiconductor devices, and more particularly to such a photoresist pattern forming method capable of improving a critical dimension uniformity by predetermining an exposure time depending on a variation in a reflection factor generated during an exposure of a photoresist film.
2. Description of the Prior Art
As a conventional technique for predetermining an exposure time for forming a photoresist pattern, there has been known a method involving, in formation of patterns with a critical dimension by the unit of a lot (including 24 wafer sheets or 48 wafer sheets), preparing a photo latitude curve as shown in FIG. 1 on the basis of one wafer optionally selected from each lot, deriving an exposure time by use of the photo latitude curve, and applying the exposure time to all wafers of the lot.
In accordance with this method, however, patterns may be non-uniformly formed due to a coating thickness difference between lots or between wafers or a variation in a reflection condition of a substrate. As a result, a non-uniformity problem may occur.